Mail-processing machines such as postage meters are now in common use in firms and in post offices.
Postage meter manufacturers are seeking to make postage meters increasingly sophisticated to satisfy the needs of users of such machines. In particular, a concern of manufacturers is to make machines that offer a large number of features to users.
Increasing the number of features or control functions offered by a postage meter involves increasing the number of control motors required to implement such features. In general, such motors are DC motors.
Currently, such control motors are powered by a DC electrical power supply of a conventional type comprising a rectifier, a primary circuit and a secondary circuit. To satisfy the above-mentioned needs of users, it is therefore necessary to provide a DC power supply that is adapted to supplying high enough energy to all of the control motors. As a result, the greater the number of control motors to be served, the heavier and bulkier such a DC power supply becomes.
Furthermore, postage meters must be approved before they can be put into service. Such approval involves the presence of a safety locking circuit connected to a cover switch of the machine and co-operating with the electrical power supply. The function of the safety locking circuit is to switch the electrical power supply off whenever the cover of the machine is open. Certain regions of the machine that are accessible to an operator whenever the cover is open might be potential sources of mechanical and electrical danger.
Currently, a circuit approved under UL, CSA, and BSI standards consists of an electromechanical device, such as a switch or a relay, which is itself approved, and which is wired in series with the power supply. It may be situated upstream from, downstream from, or within the power supply. The increase in the number of control motors then means that the electromechanical component used must be bulky and costly because it needs to have a high current-interrupting capability.
Postage meter users expect postage meter manufacturers to produce postage meters that are as compact as possible so that they can be used as office equipment.